Tension-maintaining device for cranes and the like



TENSION-MAINTAINING DEVICE FOR CRANES AND THE LIKE Filed Feb. 18. 1957April 7, 1959 H. ERNST ET AL 2 Sheets-Sheet 1 INVENTORS HELLMUT sklvsrRUDOLF ZAPP ERNST KROP/K ATTORNEYS April 7, 1959 H. ERNST ETALTENSION-MAINTAINING DEVICE FOR CRANES AND THE LIKE Fil'ed Feb. 18, 19572 Sheets-Sheet 2 IN VENTORS HELLMUT ERNST RUDOLF ZAPP ATTORNEYS UnitedStates Patent TENSIOJ. -MAINTAINING DEVICE FOR CRANES AND THE LIKEHellmut Ernst, Rudolf Zapp, and Ernst Kropik, Nurnberg, Germany,assignors to M.A.N. Maschinenfabrik Augsburg-Numberg AG, Nurnberg,Germany Application February 18, 1957, Serial No. 640,842

7 Claims. (Cl. 254-172) The present invention relates to a tensionmaintaining device for cranes and the like, and more particularly tosuch a device which is secured to a downwardly directed end of the cranelifting line to exert a pulling force on the lifting line whenever saidline tends to become slack.

It is the principal object of this invention to provide an inexpensivetension maintainng device for cranes and the like, which requires aminimum of space and may be installed on existing cranes.

It is another object of this invention to provide a tension maintainingdevice for cranes and the like which becomes effective immediately onany slackening of the lifting line.

It is a further object of this invention to provide a tensionmaintaining device for cranes and'the like which requires relatively lowforces to prevent the occurrence of slack in a crane lifting line.

It is an additional object of this invention to provide a tensionmaintaining device for cranes and the like which essentially comprises aweight which readily descends under the action of gravity when any slackoccurs but is immediately braked against upward movement when thelifting line is lifting a load.

It is still another object of this invention to provide a tensionmaintaining device for cranes and the like wherein a tension elementwill pull said lifting line to maintain said lifting line taut wheneverthe force exerted by a load on said lifting line is suddenly decreased.

Other objects and advantages of this invention will become apparent uponreference to the accompanying description when taken in conjunction withthe following drawings wherein- Figure 1 is a side elevational view ofan embodiment of the tension maintaining device of this inventionemploying a hydraulic brake with a portion of the brake shown insection; and

Figure 2 is a view similar to Figure 1, which shows another embodimentof the invention wherein a tension winch is substituted for the tensionweight and hydraulic brake of the Figure l embodiment.

The tension maintaining device as disclosed in this invention wasoriginally devised for operation on stripper cranes in steel works. Insteel making, stripper cranes are used for transporting ingots and moldsin which the ingots are cast. When equipped with a tong head having apressure piston, stripper cranes are also used for removing the ingotsfrom the molds after they have become set.

In the ingot removing operation, the mold is seized by the tongs of thetong head while the piston exerts a force against the ingot. One end ofthe mold is set upon a surface so that when the ingot emerges from themold, the ingot will be in contact with the surface and will not bedropped upon a surface. The mold, however, will be quickly jerked upwardbecause of the release of the ingot from the mold. The upward movementof the tongs will cause a sudden slackening of the lifting line whichsuspends the tong head.

Slack also can occur in stripper and other types of ice cranes when theload on the crane is being lowered to a surface and reaches the surfacebefore the crane operator has stopped the continuing downward movementof the crane line upon which the load is suspended.

The sudden slackening of the crane lifting line results in a whipping ofthe line which is dangerous since it may cause damage to equipmentwithin the plant or may result in injury to operating personnel. Inaddition, the sudden forces exerted upon the whipping lifting line causea gradual weakening of the line which greatly decreases the operatinglife of the line. The expense involved in frequent replacement of thelifting line is undesirable, since it adds greatly to the operatingcosts of the crane.

The present invention comprises a tension maintaining device for a craneline and prevents the occurrence of slack in the crane line by exerting'a pulling force upon the line. This device essentially comprises atension weight attached to a braking device. The tension weight issecured to a downwardly directed end of the lifting line of the craneafter it has passed over the lifting pulley block and idler pulleys. Theoccurrence of any slack in the lifting line will cause an immediatedownward movement of the tension weight, under gravity, to exert apulling force on the lifting line to eliminate the slack. However,whenever a force is exerted upon the line by the lifting of the load bythe line, the upward movement of the weight is braked by a hydrauliccylinder or a tension winch. Both of the embodiments comprising thehydraulic braking cylinder and the tension winch will be described.

Referring now to Figure 1 wherein like reference symbols indicate thesame parts throughout the various views, 1 indicates the frame of anoverhead traveling crane having a lifting drum 2 thereon. A cranelifting line 3 has one end wound around the lifting drum and the otherend passing around a pulley 4 in the lifting block 5 which has atransverse bar 5A to which a tong head may be attached. The line thenpasses upwardly over an idler pulley 6 and then downwardly so that thedownwardly directed end 7 of the lifting line is connected to a tensionweight 8. The tension weight 8 is normally in contact with a resilientbuffer stop 9 which is mounted on the lower surface of the frame 1.

The other end of the tension weight 8 is connected to a hydraulic brake,generally indicated at 10, which is mounted upon structure extendingfrom the overhead frame 1. The brake 10 comprises a piston rod 11 oneend of which is connected to the tension weight 8 and the other end isconnected to a piston 12 which reciprocates within a brake cylinder 13.Check valves 14 are provided in the piston 12.

The brake cylinder 13 is open at both the upper and lower ends, asindicated at 15 and 16, respectively, and has a conduit 17 whichprovides communication between both ends of the brake cylinder. Theconduit 17 has a check valve18 therein. The check valve 18 is operablein the same direction as the check valves 14. The open end 16 of thebrake cylinder is connected through a conduit 19 to a balancing chamber20 which is open to the atmosphere. The balancing chamber, conduits andthe brake cylinder are filled with a hydraulic fluid indicated at 21 tothe level as shown in Figure 1.

Mounted upon the piston rod 11 is an actuator arm 22 which engages aswitch 23 which is connected with the operating circuit of the liftingdrum 2. The switch 23 is acutated by increasing slack in the liftingline which causes the tension weight to descend beyond the switch 23.Actuation of the switch will disengage the lifting drum from itsoperating circuit to prevent addi tional slack forming in the liftingline.

' With the above description of the embodiment of the invention in mind,the operation of a tension main taining device will next be described.

The load which is supported from the transverse bar of the lifting blockwill maintain. the line taut when the load is being raised or lowered.However, as soon as the load is-supported byany means whatsoever, theforce exerted upon the lifting line by the load, suddenly will decreaseand the lifting line will become slack. The slackening of the line willdecrease the force exerted through the lifting line on the tensionweight. Consequently, the tension weight 8 will immediately descendunder the force of gravity to take up the slack in the lifting line. Thepiston 12 will correspondingly move downwardly with the tension weightvsince the check valves 14 will be open as shown in Figure 1 to permitthe hydraulic fluid to flow through the piston. As a result theresistance upon the piston by the hydraulic fluid will be negligible.Should the piston approach the lower end of the brake cylinder beforethe load acts upon the lifting line to tighten up the line, the switch23 will be actuated and will stop rotation of the lifting drum.Therefore, even if the tension weight 8 cannot move further downwardlyno additional slackening will occur in the lifting line.

When the full force of the load is again exerted upon the lifting line,the line will move the tension weight 8 upwardly. This upward movementof the tension weight will cause a corresponding upward movement of thepiston 1-2. This upward movement of the piston will be considerablyslowed, however, since the check valves 14 and 18 will be closed so asto prevent the circulation of fluid through the piston. Therefore, thetension weight 8 will slowly move upwardly until it is stopped bycontacting the buffer stop 9. When the tension weight 8 contacts thebuffer stop it will be moving at a rather slow speed because of theaction, of the braking cylinder and hence, there will be very littleshock in the crane structure.

Proceeding next to the embodiment shown in Figure 2, the hydraulicbraking cylinder and tension weight of Figure l is eliminated and atension winch indicated generally at 24 is substituted therefor. Thewinch 24 is guided along a vertically extending rack 25 which isconnected with the crane frame 1. The winch 24 has a pinion 26 which isin mesh with the rack 25. The pinion 26 is connected on a shaft 27 uponwhich, is also connected a gear 28 which is engaged by a ratchet 29. Thegear 28 is drivingly connected to a winch tension motor 30 throughgearing indicated at 31.

Inthe operation of the embodiment in Figure 2, the entire tension winch24 will move downwardly on the rack 25 when any slack occurs in thelifting line. However, when force is exerted on the lifting line by theload so as to cause an upward movement of the tension winch, the pinion26 is connected with the tension motor 30 by the ratchet 29 and the gear28 so that the upward movement is braked by'the tension motor. Thisbraking will occur throughout subsequent movement of the tension winchuntil the winch engages the buffer stop 9. Thus, it can be seen that theembodiment of Figure 2 functions in the same manner as the embodiment inFigure l, except-for the fact that in the Figure 2 embodiment braking;is accomplished by a winch and in Figure 1= braking is accomplished by ahydraulic cylinder.

Various modifications maybe made in each of the embodiments in Figures 1and 2 without departing from the scope of the invention. For example,the hydraulic brake in, Figure 1 could be replaced by a pneumatic brake.In addition, the invention is not restricted to stripper cranes buttoany typeof crane where there is any danger of a slackening inthelifting line.

Thusit can be seen that the tension maintaining device ofthepresentinvention is extremely'simple in operation and, requires little roomsince it is fastened on a downwardly directed end of the lifting line.The principal action of the tension, maintaining device to eliminateslack in the lifting line is under the force of gravity. This devicewill therefore act with extreme speed and with a minimum of delay andwill prevent the accumulation of slack in the line. In those rareinstances where the slack occurs so suddenly that it cannot be properlyeliminated by the device, the rotation of the lifting drum will bestopped under the action of a switch as previously described.

An additional advantage of this invention is the dis covery thatrelatively low forces are necessary to prevent the slackening in a cranelifting line. The slack in the line is eliminated essentially by astretching of the lifting line under the exertion of a pulling force bya tension element. Furthermore, the tension element is. provided with abraking device which so operates that the force exerted by the brakingdevice on the lifting line during a slackening movement of the line isconsiderably smaller than. theportion of the load acting upon the line,whereas during the movement of the lifting rope which tends to stretchthe rope, the power exerted by the braking device is almost equal tothat portion of the load acting upon the lifting line end. In employingthis tension maintaining device, the total weight of the crane isincreased by only a small amount but slackening of the crane line iseffectively eliminated. Furthermore, the tension device is so related tothe crane that there will be no undue rapid lowering of the load so asto endanger personnel or equipment. In all likelihood this would be thecase if too little tension were exerted by the tension maintainingdevice during any lowering of the load.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions and,accordingly, it is desired to comprehend such modifications within thisinvention as may fall within the scope of the appended claims.

What is claimed is:

1. In a crane, a lifting drum, a lifting pulley block, a line having oneend wound around said lifting drum and the other end passing around saidblock pulley with. said other end of the line being directed downwardly,means on said line other end for exerting a pulling force on said lineto maintain said line under tension, and a braking de vice connected tosaid tension maintaining means to exert a force considerably smallerthan the load acting on the rope when said rope other end is being movedin a direction which tends to stretch the same but which exerts a forcealmost equal to the load exerted on the lifting rope during the movementof the lifting rope which tends to slacken the rope.

2. In a crane, according to claim 1, wherein said braking devicecomprises a hydraulic pressure cylinder.

3. In a crane, a lifting drum, a pulley block, a lifting line having oneend wound around said drum and the other end passing around said blockpulley with said other end being directed downwardly, a tension weighton said downwardly directed end to maintain said line under tension, anda brake attached to said tension weight for braking the upward movementof the tension weight but enabling the tension weight to move downwardlyunder the force of gravity.

4. Ina crane, according to claim 3, with said brake comprising acylinder, a piston slidably mounted within said cylinder and having oneend attached to said tension weight, valve means interconnecting bothsides of said piston and operable only when said piston is movingupwardly so as to brake the upward movement of the tension weight but toopen when said piston is moving downwardly to enable said tension weightto descend under the force of gravity.

5. In a crane, as claimed in claim 4, with said brake cylinder beingconnected to' a balancing chamber which is open to the atmosphere.

6. In a crane, a lifting drum, a pulley block, a line having one endwound around said lifting drum and the other end passing around saidpulley block with said other end being directed downwardly, means onsaid other end of said lifting line movable upwardly and downwardly forexerting a pulling force on said line to maintain said line undertension, and a switch actuated by the downward movement of said tensionmaintaining means for stopping the operation of said lifting drum.

7. In a crane, a lifting drum, a lifting pulley block, a line having oneend wound around said lifting drum and the other end passing around saidblock pulley with said other end of the line being directed downwardly,means on said lines other end and movable upwardly and downwardly forexerting a pulling force on said line to maintain said line undertension, and a braking device connected to said tension maintainingmeans to exert a force considerably smaller than the load acting on therope when said tension maintaining means is being moved in a directionwhich tends to stretch the same but which exerts a force almost equal tothe load exerted on the lifting rope during the movement of the tensionmaintaining means which tends to slacken the rope.

References Cited in the file of this patent UNITED STATES PATENTS757,211 Mann Apr. 12, 1904 2,131,133 Babson Sept. 27, 1938 2,463,394King Mar. 1, 1949

